Time to start controlling plants in Iowa ponds

According to the Iowa Department of Natural Resources, now is the time to start controlling the growth of underwater plants in the state’s ponds.

Pond plant growth is not exactly the same from year to year; if there were problems using the pond last year, chances are the same problems will exist this year. A healthy pond needs an aquatic plant habitat, but too much of a good thing may need to be controlled.

In an existing Iowa pond, mechanical and chemical vegetation control are the best options and are generally most effective if you start early, when plant growth is not at its maximum level.

Waiting until growths are thick will make control difficult, take longer and could result in water quality issues that harm fish.

Mechanical methods include bottom-blanketing, shading, removal and water draw-down.

Private ponds can be temporarily blanketed with weed barrier products or thick black plastic (punctured to allow gases to escape) weighted and left in place for 30 days early in the season to inhibit plant growth in fishing and swimming areas.

Drawing down the pond’s water level in the summer or winter to expose aquatic plants to drying and freezing conditions to limit their growth in future months.

Herbicides will control pond vegetation chemically. Follow these five steps with any herbicide application:

• Correctly identify the plant to be controlled.

• Measure the area to be treated (surface area and depth.

• Read the herbicide label to determine the correct timing and amount to apply.

• Identify potential restrictions on uses of the water (irrigation or watering animals.

• Apply according to label directions.

All aquatic herbicides produce the best result if applied on a calm, sunny morning. Granular herbicides are attractive because of their ease of application, but many granular products are 2,4-D-based and are only effective on broadleaf plants. Most aquatic plants are in the grass family, so the 2,4-D products will not be effective.

Most underwater plants can be killed with any diquat-based product. Algae and a few underwater plants can be treated with copper-based herbicides; some of these are granular.

Application of liquid herbicides to underwater plants requires that the liquid be applied underwater to be in contact with the plants. It kills by contact, and is not as effective if sprayed on the water’s surface or (for diquat) applied in muddy water.

An active ingredient that does well in muddy water is endothall. More information on aquatic plant identification and some of these methods can be found on the Department of Natural Resources website. Go to www.iowadnr.gov and search "pond plants."